1. Field of the Invention
The present invention relates to an arrangement for coupling an rf-SQUID to a superconducting tank circuit and to a base plate, in which arrangement of the tank circuit and the rf-SQUID form a coplanar structure and the tank circuit has a slit.
2. The Prior Art
Various proposals have been pursued heretofore for coupling rf-SQUID magnetometers to superconducting tank circuits.
One possibility is to employ a lambda resonator, to which an rf-SQUID is coupled galvanically, whereby said rf-SQUID functions at the same time as a flux pickup loop. Such a SQUID magnetometer may have a tank frequency of 3 GHz.
The use of a lambda resonator, however, is problematic in that it has a quality of only a few 100, which represents a quite low quality in view of the fact that qualities of a few 1000 have already been obtained with lambda/2 resonators. Furthermore, the fact that it is necessary in view of the galvanic coupling to take into account also a parameter which is difficult to calculate, namely the high-frequency current distribution, leads to considerable problems as well. The high-frequency current distribution represents a quantity which is not easy to calculate or control by experimentation. Therefore, it is difficult to optimize the SQUID layout.
Another possibility is to produce planar LC-tank circuits from YBaCuO thin layers with high frequency and high quality. Such LC-tank circuits are operated in a flip-chip arrangement, with the rf-SQUID in washer-SQUID structure. The parasitic capacities occurring in this connection between the LC-tank circuit and the rf-SQUID reduce the quality of the LC-tank circuit and make the current distribution in the combined LC-tank circuit/washer-SQUID structure complicated.
The aforementioned arrangement has been described by this applicant in application 196 11 900.6, which is still unpublished. Said arrangement solves the problem of parasitic capacities. However, the problem continues to exist that the coplanar arranged rf-SQUID and tank circuit cannot be arranged in one plane with the base plate, and that the base plate, furthermore, represents a potential noise source that may limit the application of an rf-SQUID magnetometer.